Joining polymer to aluminium by Through Hole Extruded Friction Stir Spot Welding

Abstract

The demand of joining dissimilar materials is increasing in several industries with growing need for lightweight design solutions. The increasing environmental concerns, cost reduction and low fuel consumption requirement in transport industries are pushing the need for optimized structural components integrating multiple materials, where polymer-based components and aluminium alloys play an important role. With the limitations that exist, with the currently available joining processes, to join polymers and composite to metals, the work presented here aims at introducing the development and evaluation of a new efficient solution for joining these materials.

Two new dissimilar material joining process, Through Hole Extruded – Friction Spot Welding (THE-FSpW) and Through Hole Extruded – Friction Stir Spot Welding (THE-FSSpW), are implemented and tested in joining polymer to aluminium alloy. These two processes share the same concept. The concept is the utilization of a rigid thin extrusion die plate positioned in the middle an overlapped joint formed by aluminium alloy plate over the polymer. This extrusion die plate has at least one through-hole (or slot). The metallic component will be pushed through the hole in THE-FSpW (or slot, in THE-FSSpW) into the polymer component, by a non-consumable, rigid rotating tool. The stirred visco plasticized aluminium that is forced to pass through the hole in the extrusion die plate will flow into the polymer forming a hook. Mechanical locking and adhesive bonding mechanism are achieved in between these dissimilar materials forming the joint. This new solution has distinct benefits in comparison with the existent alternatives and arrives in a moment when the perceived need, and market, for these metal-to-polymer joints is growing. The tested metals are AA5754-H111 and AA2024-T351 with 6 mm thick. The polymers are plates with a thickness of 10 mm, made of PEEK and Polyamide 6. The rigid thin extrusion die plate is AISI316 with 1 mm thick.

The implementation of these two solid-state joining process involved: tool design, development of experimental setup and process parameters. Tool design and development of experimental setup have a critical role in the application of any solid-state joining process. The influence of process parameters on joint hook geometry is studied, and a set of optimal parameters is established for the tested base materials. To analyze the joint, mechanical, microstructural and geometrical tests are conducted. For both processes, the joint formation was repeatable and controllable. From the analysis of both joining processes the THE-FSSpW process shown better joint hook geometry with an average thickness of 1.9 mm, delivering a tensile shear load bearing capacity of 7.3 kN. The hook from THE-FSpW process presented an average thickness of 1.4 mm, and the joint reached a tensile shear load bearing capacity of 2.3 kN.